CSSOM - the CSS Object Model - is the set of APIs that allow manipulation of CSS from Javascript. It is similar to what DOM is for HTML. It allows users to read and write CSS style dynamically.
AnimationEventCaretPositionCSSCSSConditionRuleCSSCounterStyleRuleCSSFontFaceRuleCSSFontFeatureValuesMapCSSFontFeatureValuesRuleCSSGroupingRuleCSSImportRuleCSSKeyframeRuleCSSKeyframesRuleCSSMarginRuleCSSMediaRuleCSSNamespaceRuleCSSPageRuleCSSPositionTryRuleCSSPositionTryDescriptorsCSSRuleCSSRuleListCSSStartingStyleRuleCSSStyleDeclarationCSSStyleSheetCSSStyleRuleCSSSupportsRuleFontFaceFontFaceSetFontFaceSetLoadEventMediaListMediaQueryListMediaQueryListEventScreenStyleSheetStyleSheetListTransitionEvent